Typically, vehicles having a heading system, such as aircraft having an attitude and heading reference system, or AHRS, must be periodically calibrated to ensure a minimization of measurement errors due to such factors as hard iron disturbances of the aircraft, or other vehicle, such as a ship, having a heading system containing a magnetometer. Most such prior art calibration methods require numerous repositioning of the vehicles, such as the aircraft, such as eight or more different positions, to come up with an approximate calibration number. None of the prior art methods known to applicant utilize theoretical magnetic field properties of the Earth, such as theoretical values for horizontal and vertical intensity of the magnetic field at the location of the positioned vehicle, such as the aircraft on the tarmac, for comparison with actual magnetometer readings at such a position, thereby increasing the complexity of the calibration procedure and, potentially, affecting its accuracy. Examples of such prior art methods are disclosed in U.S. Pat. Nos. 7,587,277; 8,061,049; 7,891,103; 7,146,740; and 6,860,023, none of which use the theoretical magnetic components of the Earth's magnetic field, such as obtained from a web site, to calibrate the AHRS heading. By utilizing the calibration method of the present invention, this calibration procedure is significantly simplified and is an improvement over prior art methods.